1. Field of the Invention
The present invention relates generally to a planar stage moving apparatus for a machine and, more particularly, to a planar stage moving apparatus for a machine that enables reduction of the size of a table transfer system and accurate transfer of a table provided in a machine such as a milling machine by moving the table using an electromagnetic force.
2. Description of the Related Art
An apparatus for carrying out a necessary operation while a table positioned on a base is being moved by a separate transfer unit provided for a machine tool or a measurement tool used in the industrial field. In particular, a machine tool such as a milling machine or a wire cutting machine that has a tool fixed to an upper portion of a table to machine a work piece is provided with a table moving unit for moving the table under the control of an NC controller.
A general table moving unit for a machine converts rotational force generated by an electric motor to linear movement forces to move a table, i.e. a movable body with respect to a base, i.e. a fixed body. Accordingly, when a table needs to be moved transversely (in the X-axis direction) and longitudinally (in the Y-axis direction) as in a machine tool such as a milling machine, it is necessary for the machine tool to separately include a movement shaft for transverse movement of the table and a movement shaft for longitudinal movement of the table, in which case the structure of a table moving unit is complex and large-sized.
The applicant of the present invention has already developed “a miniaturized stage apparatus using a permanent magnet driven linear motor and an air bearing” to improve the shortcomings of a table moving unit applied to a general machine. FIGS. 1A and 1B are views schematically illustrating Korean Patent Laid-Open No. 10-2007-0052524 titled “a miniaturized stage apparatus using a permanent magnet driven linear motor and an air bearing” and filed by the applicant of the present invention.
As illustrated in FIGS. 1A and 1B, a stage moving apparatus 100 includes a base 200, i.e. a fixed body and a table 300, i.e. a movable body. A linear (grid) encoder 600 for detecting movement of the table 300 is fixed to one side of the base 200. In particular, guide walls 210 and 310 are formed on both sides of the base 200 and the table 300 as illustrated, and motor mounting spaces 220 and 320 for mounting the linear motor 400 that provides a movement force to the table 300 are formed inside the base 200.
The linear motor 400 includes a stator core 420 on which a coil 410 is wound and a mover core 440 to which a pair of permanent magnets 430 are attached. When current flows through the coil 410 with permanent magnets formed on both sides of the linear motor 400 creating magnetic fields, the direction of a force is determined according to the directions of the current and magnetic fields. In other words, if current is applied to the coil 410, after the direction of a force is determined according to the direction of the current flowing through the coil 410, the table 300 is moved in a direction on the base 200. To achieve this, the direction of the current flowing through the coil 410 is arbitrarily controlled so that when the direction of the current applied to the coil 410 is reversed, the direction of force can also be reversed.
A pre-pressure is applied to prevent the table 300 from being separated from the base 200 and increase the strength of an air bearing during movement of the table 300 by the transfer force of the linear motor 400 using a magnetic force applied between the permanent magnet 430 of the linear motor 400 and the stator core 420 as an attractive force.
An air bearing unit 500 for preventing friction and interference during movement of the table 300 on the base 200 by the transfer force of the linear motor 400 is provided between the base 200 and the table 300. The air bearing unit 500 includes a plurality of air pads 510 fixed to a surface of the table facing the base 200 and air supply lines 520 for supplying a pneumatic pressure to the air pads 510 respectively. The directions of a repulsive force applied between the base 200 and the table 300 and an attractive force applied between the permanent magnet 430 of the linear motor 400 and the stator core 420 during the operation of the air bearing unit 500 are opposite to each other, and the magnitudes of the forces are the same, whereby the forces are in an equilibrium state so that when the transfer force by the operation of the linear motor 400 is transferred to the table 300, the table can be stably moved on the base 200.
As mentioned above, during movement of the table 300 by driving of the linear motor 400, the position of the table 300 is measured by the linear encoder and the table 300 is accurately controlled by an NC controller (not shown).
However, in the above-mentioned stage moving apparatus, since movement of a table is restricted only in one linear direction, the installation space for a movement unit for movement of the table needs to be increased to apply the stage moving apparatus to a machine tool such as a milling machine that requires movements in the transverse direction (X-axis direction), the longitudinal direction (Y-axis direction), and an angular direction. Furthermore, when two transfer shafts for X-Y axis transfer are stacked, the height of the entire stage increases and the strength of an upper portion of the stage decreases.